The present invention relates to catheters and/or source wires and/or radioactive stents for treatment of a stenosis within a bodily conduit. More particularly, the present invention relates to a catheter and/or source wire and/or radioactive stents further comprising an energy filter.
Percutaneous Angioplasty (xe2x80x9cPTAxe2x80x9d) is presently an effective treatment for the severely occluded coronary artery. A significant problem with angioplasty, however, is the reoccurrence of the occlusion. Post re-occlusion often necessitates additional PTA. Becker et al., Radiofrequency Balloon Angioplasty, Rationale and Proof of Principle, Investigative Radiology, (November 1988), p. 810.
It has previously been suggested that radiation applied in appropriate dosages retards smooth muscle proliferation that is characteristic of restenosis. Various techniques have been developed to treat restenosis in bodily conduits using catheters and radioactive materials. One such technique includes introducing a catheter to the treatment site, positioning radioactive material inside the catheter for a specified period of time, and removing the radioactive material and catheter from the conduit after the allocated time period. Bottcher et al., Endovascular Radiation xe2x80x94A New Method to Avoid Recurrent Stenosis After Stent Implantation in Peripheral Arteries: Technique and Preliminary Results, International Journal of Radiation Oncology, Biology and Physics, Vol. 29, No. 1, Pages 183-186 (1994).
U.S. Pat. No. 5,059,166 to Fischell et al. discloses the positioning of radioactive intra-arterial stents at a treatment site for the reduction of restenosis in the vasculature, wherein the radioactive material is an alpha, Beta or Gamma emitter.
U.S. Pat. No. 5,302,168 to Hess describes a method and apparatus for reducing restenosis wherein radioactive material is included within the distal end of a treatment catheter, on the exterior of a catheter or included on an expandable stent positioned on the exterior of a catheter for radiation treatment of the stenosis. The patent to Hess further describes an embodiment wherein a selective energy shield is positioned over the radioactive material that is operatively connected to the catheter such that during positioning of the catheter, the shield, when positioned over the radioactive material, blocks the emitted radiation until needed.
U.S. Pat. Nos. 5,840,064 and 5,947,924 to Liprie, the disclosures of which are herein incorporated by reference, describe a method and apparatus for treating a stenosis including advancement of a source wire through a treatment lumen in a catheter equipped with dilation and/or centering balloons for controlled irradiation of the stenosed region. U.S. Pat. Nos. 5,503,614 and 5,857,956 to Liprie, the disclosures of which are herein incorporated by reference, disclose flexible source wires for radiation treatment of a stenosed site wherein the source wire includes an encapsulated radioactive source provided in a housing tube, and a flexible backbone inserted within the housing tube.
When treating restenosis or other diseases inside a bodily conduit, such as a blood vessel, with a radioactive source, often it is very important to precisely control how that emitted radiation affects the various exposed vessel tissues. It is known that ineffective treatment of vessel walls will generally occur where a radiation source rests near a vessel wall rather than in a position offset from the vessel wall. The art further recognizes that uneven irradiation of tissue is particularly problematic within the tortuous regions of the vasculature. Thus the art emphasizes the need to effectively center, or at least offset, the radioactive source within the vessel to prevent ineffective radiation delivery to the target site.
Depending on the location of the diseased area, often the radioactive source must stay in the blood vessel several minutes (5-20 minutes, or longer) to ensure that the proper radiation dose is delivered to the treatment site. Excessive radiation can promote hyperplasia at the target site rather than reduce smooth muscle proliferation. Accordingly, the exposure time is calculated with regard to the portion(s) of the vessel wall receiving the greatest dose. If the catheter design does not provide for catheter offset, the difference in tissue adsorptions can be profound, and an ineffective dose will be delivered to the remainder of the treatment site. For example, the target site away from the radioactive source can adsorb something on the order of 15 Gray (Gy) while the intima (i.e., the portion of the blood vessel wall proximal to the radioactive source) adsorbs 100 Gy or more.
Centering provides some measure of control, wherein the source wire is positioned as far away from the inner vessel wall as possible. Damaging surface activity/exposure to portions of the vessel wall is thus reduced while the proper radiation dose is delivered to the treatment site. One method of distancing the source from the vessel wall is described by U.S. Pat. No. 5,863,284 to Klein and U.S. Pat. No. 5,910,101 to Andrews et al. These patents describe a technique whereby a balloon is inflated on the catheter housing to center the radioactive material. The patents teach the importance of centering the radioactive source within the bodily conduit at the stenosed site, particularly under circumstances where treatment occurs within the tortuous regions of the vasculature.
Another method for positioning the source away from the inner vessel wall includes use of a thick walled catheter, wherein the thickness of the catheter wall is such that the catheter""s overall profile approximates that of an inflated balloon catheter. The thick walled catheter embodiment similarly recognizes the importance of offsetting the radioactive source from a vessel wall such that portions of the vessel intima do not excessively adsorb radiation.
Balloons and thick walled catheters, each useable to offset or center a source, provide limitations that compromise treatment. Centering balloons must be inflated during the entire treatment phase. The area occupied by the inflated balloon inside the lumen greatly reduces blood flow. Although there are many different shapes of balloons, the volume of the inflated balloon combined with the narrow lumen opening and the irregular plaque shape, all add up to constrict or greatly diminish blood flow, which can be problematic for the patients. Both the inflated balloon and the thick walled catheter occlude the vessel opening either to totally block or greatly limit blood flow during treatment. Since treatments can last 5-20 minutes or longer, it is often necessary to remove the radioactive material and devices so greater perfusion can take place. Once blood flow of the patient is restored, the devices are repositioned and the treatment is resumed where it left off. In some patients due to the decreased perfusion, the treatment is interrupted several times before the total dose of radiation is delivered.
Use of a balloon to center or offset a catheter adds complexity to the catheter and increases the complexity of the treatment procedure with regard to overall procedure duration, taking into account the need for interruption and resumption of treatment to allow perfusion. Increased device complexity and operation time translates disadvantageously to increased overall cost of the medical procedure. What is needed in the art is an effective method for delivering an even radiation dose to the treatment site without the need for a catheter centering balloon.
Another limitation of current methods and devices includes the inaccessibility of the smaller vessels, where the openings are too narrow for the thick wall catheter and/or inflated balloon catheter to fit. A partially-inflated balloon catheter or a thinner wall catheter may allow access to these smaller vessels, but does not solve the problem of off-center irradiation of the inner vessel wall. Clinically, treatment of the patient would either not be possible or not be practicably effective.
Accordingly, there remains a need in the art for a catheter system that provides an even radiation dose to a treatment site, including treatment sites located in the smaller blood vessels, without overly occluding blood flow.
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the energy filtering system of the present invention. The energy filtering system includes an energy filtering material provided between a radioactive material and a treatment target such that radioactive energy is filtered. In a preferred embodiment, the filtering material is provided as a thin-walled layer, such as a micro-foil, mesh, helically wound spring, film, coating or stackable right-angle disks, among others, at one or more locations between the radioactive source and a treatment target, to filter the radiation energy during treatment.
The filtering material may be a high-density material, such as platinum, applied or incorporated in a supporting structure between the radioactive material and the treatment target. The supporting structure may include a catheter having a treatment end, a source wire movable within the catheter or a combination of both. Alternatively, the energy filter may be affixed to a radioactive stent disposed at the treatment site.
In one embodiment, the energy filter is disposed at the distal end of a catheter containing a radioactive source. The filter substantially surrounds the source, selectively passing energy from the source to the target area needing treatment.
In another embodiment, the energy filter is disposed at the distal end of a source wire movable within a catheter. The source wire contains a radioactive source. The filter substantially surrounds the source, selectively passing energy from the source to the target area needing treatment.
In another embodiment, the energy filter is disposed in both the treatment end of a catheter and at the distal end of a source wire movable within the catheter. The energy passes from the distal end of the source wire through a first filter material on the source wire and then through a second filter material disposed on the catheter, thereby selectively passing energy from the source to the target area needing treatment.
In another embodiment, the energy filtering material is disposed on a stent containing a radioactive source. The filter material is disposed between the radiation source and the treatment site, thereby selectively passing energy from the source to the target area needing treatment.